Method and means for controlling resuperheat temperature



Sept. 16, 1958 A. BURl 2,852,005

METHOD AND MEANS FOR CONTROLLING RESUPERHEAT TEMPERATURE Filed Jan. 26, 1955 2 Sheets-Sheet 1 I N VEN TOR.

lqLf EED BUR].

BY Kiw- Sept. 16, 1958 Filed Jan. 26, 1955 2 Sheets-Sheet 2 Fig. 2

INVENTOR. A LF'EED 51/121.

ATTORNEK Unite tat-cs lVIETHOl) AND MEANS FGR CONTROLLING RESUPERHEAT TEMPERATURE Alfred Buri, Winterthnr, Switzerland, assignor to Sulzer Freres, Societe Anonyme, Winterthur, Switzerland, a corporation of Switzerland Application January 26, 1955, Serial No. 484,110

Claims priority, application Switzerland January 28, 1954 6 Claims. (Cl. 122479) There are several conventional methods for maintain ing the temperature of resuperheated steam at a predetermined value. Swinging burners have been proposed, for example, affording change of location of the zone of utmost heat supply. Changing the position of the swinging burner considerably afiects other heating surfaces, so that additional control devices must be provided in other parts of the steam generating and superheating plant with which the resuperheateris combined. It is not possible to simultaneously control two resuperheaters with swinging burners. It has been proposed to place resuperheaters in separate ducts which form a flue gas channel and to provide dampers for inhibiting the flow of hot gases through the ducts. By changing theamounts of combustion gases flowing through the individual ducts the temperature of the steam resuperheated in the resuperheaters arranged in the ducts is also changed. The

last-mentioned arrangement is expensive and is not satisfactory for modern steam generating plants in which the resuperheaters are preferably exposed to radiant heat, i. e. are arranged within or close to the combustion chamber. Injection of water into the resuperheater reduces the thermal efiiciency because the injected water must be evaporated and superheated without doing work in the high pressure part of a steam turbine. Injecting water may cause salt deposits in the resuperheater and in theturbine. The resuperheater may be composed of two parts and a steam, cooler may be interposed between the two parts. This involves special equipment and arrangements for removing and making use of the heat taken from the steam by the steam cooler. It has also been proposed to control the temperature of the partly expanded steam by arranging an indirectly steam heated regulating resuperheater upstream of a combustion gas heated resuperheater.

Such regulating resuperheaters must be very large, so that they can transfer the missing heat to the partly expanded steam at all operating conditions. When providing a regulating steam-heated resuperheater in addition to a gas heated resuperheater, the heating surface must be almost doubled and steam or other heating fluid of a rather high temperature must be used, so that a regulating resuperheater is used only in exceptional cases.

According to the present invention, the partly expanded steam is heated or cooled by steam takenfrom the steam generator and returned to the steam generator. The partly expanded steam is heated, if its temperature is too low, and is cooled, if its temperature is too high, in a heat exchanger which has a heating surface on one side of which flows partly expanded steam, and on the other side of which flows the unexpanded steam which is taken from the steam generator. Means are provided for changing atent in the heat exchanger.

The arrangement according to the invention has considerable advantages. The heat exchanger can be small. Because of the heat flow in both directions, wide temperature ranges can be regulated. During normal operation, i. e. when the partly expanded steamh-as the do sired temperature, no heat need be transferred in the heat exchanger, in contradistinction to an indirectly heated resuperheater which heats the partly expanded steam also during periods of normal operation. Depending on the temperature of the not yet expanded steam relatively to that of the partly expanded steam, the not yet expanded steam acts either as a heating agent or as a coolant. In

the latter case no heat is removed from thesystem and.

the cooling heat remains within the circuit of the operating fluid Without additional provisions. The device accordingto the invention is in fact a true heat exchanger and not a resuperheater. 4

Water may be injected into the unexpanded steam beforei'it exchanges heat in theheat exchanger with the partly expanded steamwhereby the amount of injected water is controlled according to the temperature of the resuperheated steam. 'In a modification of the invention, water is injected into the unexpanded steam after it has exchanged heat with the party expanded steam, theamount of injected water being controlled according to the temperature of the unexpandedsteam. The injection of water isone of the simplest methods of controlling the temperature'of steam; if it is used according tothe invention, no heat is wasted. Water may be injectedat two,

places: upstream of the heat exchangerin an amount that the temperature of the partly expanded steam is satisfactorily controlled, and downstream of the heat exchanger in an amount that aidesiredtemperature of the superheated unexpanded steam at the outlet of the steam generatoris maintained.

The method according to the invention may be per-J formed in such a manner that only a part of the .unexpanded steam produced in vthe steam generator for op erating the power plant is used for heat exchange with the partly expanded steam. In this manner, the range is widened within which the reheat temperature can be controlled. As a modification, only a part of the partly expanded steam may be made to exchange heat with the unexpanded steam. This narrows the limits within which the resuperheat temperature can be'cont'rolled, but facilitates accuracy of the regulation. The pressure drop (or loss) ofthe steam passing through the heat exchanger is reduced in both cases which is of particular advantage so far as the partly expanded steam is concerned.

The heat exchanger is preferably interposed with respect to the fiow'of the partly expanded steam between two combustion gas heated resuperheater sections. The

heating surfaces of the gas heated resuperheater sections andthe heating surfaces of the heat exchanger are so dimensioned that there 'is a favorable relation between, partly expanded steam and of the expanded steam downstream of the heat exchanger. A by-pass conduit may be arranged to conduct unexpanded steam around the heat exchanger and a throttle device may be arranged in this by-pass conduit, particularly if the by-pass conduit is connected upstream of thewater injection device in the conduit conducting unexpanded steam from the steam generator to the heat exchanger, so

' jection and heat transfer in the heat exchanger.

that hot steam may be conducted through the by-pass conduit, which steam has not been cooled by water in- The hot steam emerging from the by-pass conduit is returned to the unexpanded steam which has been cooled by water injection and/or by heat transfer in the heat exchanger. Itmay also be of advantage to provide a by-pass conduit for. conducting partly expanded steam around the heat exchanger and to arrange a throttling device in this bypass conduit. 7

The novel features which. are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself however and additional objects and advantages thereof will best be understood from the following description of an embodiment thereof when read in conjunction with the accompanying drawing, in which Fig. 1 is a diagrammatic showing of a plant according. to the invention;

Fig. 2 illustrates the temperatures at various operating conditions in the apparatus shown in Fig. l.

The same numerals designate the same parts in both figures.

Referring more particularly to Fig. l of the drawing, numeral 1 designates a condenser from which condensate ispumped by means of a pump 2 through a conduit 3 into a feed water container 4. A feed pump 5 raises the pressure of water from the container 4 to the highest operating pressure of the steam generating and. power plant and forces the water through a boiler feed pipe 6 into a first combustion gas heated heating section 7, which section is generally known as economizer. The preheated water enters a second heating surface section 8, in which the-water is-converted into steam, the steam being conducted through a conduit 9 into a third heating surface section 10' constituting a primary superheater. The unexpanded steam flows through a conduit 11 into one side of the heating surface of a heat exchanger 12 and therefrom through a conduit 13 into a fourth combustion gas heated heating surface section 14, which is the final superheater from which the superheated steam is conducted through a steam main 15 into the high pressure part 16 of aa turbine plant. The steam partly expanded in the high pressure turbine 16 flows through a conduit 17 and through a first combustion gas heated heating surface section 18 forming part of a resuperheater, to the other side of'the heat transfer surface of the heat exchanger 12; The partly expanded steam leaving the heat exchanger 12 is conducted through a second combustion gas heated heating surface section 19 forming part of the resuperheater. The resuperheated steam is conducted through a conduit 20 into the low pressure part 21 of the turbine plant wherefrom the steam exhausts through a conduit 22 into the condenser 1. The turbine plant including the high pressure part 16 and the low pressure part 21 drivesan electric generator 23.

A conduit 24 is connected with the feed water conduit 6, the conduit 24'being dividedintotwo water-injection conduits 25 and 26. 'The conduit 25 terminates inthe. conduit. 11 forthe unexpanded steam upstream of the heat. exchanger, a. flow control means: 27 being provided in. the conduit 25, which control means is regulated by impulses produced by a device which is responsive to the temperature of the resuperheated steam leaving the final resuperheating surface section 19. The second water injection conduit 26 terminates in the conduit .13" for the unexpanded steam downstream of the heat exchanger 12., the conduit 26 being provided with allow control means 29 which is controlled. by impulses: produced by two. devices, 30 and. 31, the former. being responsive. to thesteam temperature at the inlet of'the finalsuperheater. 14, and the latter being responsive to the steam; temperature at the outlet of the final superheater 14.

A relatively great portion of the unexpanded'steam taken; from the steam generator can-be conductedthrough a by-pass conduit 32, in which a throttle device 33 is provided, around the heat exchanger 12 directly into the heating surface section 14 of the steam generator for reducing the effect of the heat exchanger on the relatively high pressure steam. The throttle device 33 may be in the form of an orifice plate or of a valve which may be regulated by hand or automatically, or the like. Similarly, the partly expanded steam may be by -passed through a conduit 34 containing a valve 35 around the heat exchanger 12.

Fig. 2 illustrates the operation of the method according to the invention and of the apparatus shown in Fig. 1.

' The left side of Fig. 2 shows diagrammatically the vital parts of the system according to the invention. To. the right of this part of Fig. 2,. diagrams a, b, and c are plotted showing the temperatures of the unexpanded steam I and the temperatures of the partly expanded steam II, shown in dotted lines, as the unexpanded steam and the partly expanded steam pass in counterflow relation through the resuperheater according to the invention. When plotting the diagrams a, b, and c, it has been assumed that the temperature of the unexpanded steam in the heating sections 10 and 14 is the same at the three illustrated operating conditions.

Diagram a shows the conditions at normal operation of the plant. There is no need for additional temperature regulation by means of the heat exchanger 12. The Water injection through conduit 25 is therefore so adjusted that. the temperature of the unexpanded steam coming from the steam generator at the inlet of the heat ex-- changer 12. is approximately the same as the temperature of the partly expanded steam coming hour the. heating,

section 18 of the resuperheater. There is no heatexchange in the heat exchanger. The unexpanded steam leaving the heat exchanger is cooled once more by injection of water through the conduit 26, so that the unexpanded steam leaving the final superheater 14 has the desired temperature.

The diagram b illustrates the conditions if the temperature of the partly expanded steam II is subnormal. By injecting some water through the conduit 25 into the unexpanded steam coming from the steam generator, the temperature of this steam is slightly lowered. Because of thehigher temperature of the unexpanded steam, heat is transferred to the partly expanded steam and the temperature of the latter is brought up to the desired level. In order to ensure that the unexpanded steam which is returned to the steam generator has the desired temperature at the outlet of the final superheater 14 water must also be injected through conduit 26 into the unexpanded steam leaving the heat exchanger 12.

The diagram 0 illustrates the temperature conditions if'the temperature of the partly expanded steam is higher than normal. A relatively great amount of water is in jected through the conduit 25, lowering the temperature.

of the unexpanded steam so that heat is transferred from the partly expanded steam in the heat exchanger to the unexpanded steam, whereby the partly expanded steam is. cooled. If the temperature of the unexpanded steam leavingthe heat exchanger is too low, hot steam must be by-passed around. the heat exchanger from a point upstream of the connection with the water injection conduit 25 through the conduit 32 and introduced into the balance of the unexpanded steam leaving the heat exchanger 12 and before entering the superheater 14, so that the steam at the outlet of the superheater 14 will have the desired temperature.

The invention is applicable to plants operating atsuperand at sub-critical pressures. The invention can beused' in connection with manytypes of steam generators, such as forced flow steam generators, or natural circulation steam generators. The prime mover in' which the steam is expanded need not be a turbine; it may be any other type of engine suitable for steamoperation. It is not essential for the invention that the heat exchanger b'e' arranged between two combustion gas heated reheating sections. The heat exchanger may be interposed between the high pressure and the low pressure part of the steam power plant, either upstream or downstream of a singlesectionresuperheater. The prime mover may include more than two steam expansion stages, so that more than one reheating operation is necessary. In the latter case, each reheating stage may be provided with a temperature control by means of a heat exchanger according to the invention; however, it is also possible that only one of the reheating stages is controlled according to the invention, and the other is controlled by conventional means, for example swinging burners. If two reheating stages are controlled according to the invention, it is of advantage to conduct the unexpanded steam in parallel relation to the heat exchangers of the indivdual reheating stages and to provide water injection according to the invention for each reheating stage. Where the terms water and steam are used in the present specification and in the claims, these terms are intended to cover liquids and vapor other than water and steam.

What is claimed is:

l. A steam generating, superheating, and resuperheating plant comprising, in combination, a steam generator including tubular conduit means for evaporating and superheating an unexpanded operating medium, a resuperheater having two sections placed in said steam generator and receiving partly expanded steam, an indirect heat exchanger interposed in said tubular conduit means for flow of unexpanded operating medium through said heat exchanger and interposed between said two resuperheater sections for flow of partly expanded steam consecutively through one of said sections, through said heat exchanger for exchanging heat with the unexpanded operating medium, and through the other of said sections, a by-pass conduit connected with said tubular conduit means for by-passing unexpanded operating medium around said heat exchanger, and flow restricting means in said by-pass conduit for controlling the amount of unexpanded operating medium flowing through said heat exchanger.

2. A steam generating, superheating, and resuperheating plant comprising, in combination, a steam generator including tubular conduit means for evaporating and superheating an unexpanded operating medium, a resuperheater placed in said steam generator and receiving partly expanded steam, an indirect heat exchanger interposed in said tubular conduit means for flow of unexpanded operating medium through said heat exchanger and connected with said resuperheater for flow of partly expanded steam consecutively through said resuperheater and through said heat exchanger for exchanging heat with the unexpanded operating medium, a by-pass conduit connected with said tubular conduit means for by-passing unexpanded operating medium around said heat exchanger, a valve in said by-pass conduit for varying the amount of unexpanded operating medium passing through said heat exchanger, a water injection device connected with said tubular conduit means upstream of said heat exchanger and downstream of the connection of the inlet of said by-pass conduit with said tubular conduit means for injecting Water into the latter, and means responsive to the temperature of the resuperheated steam and connected with said water injection device for injecting water into said tubular conduit means when the temperature of the resuperheated steam exceeds a predetermined value.

3. A steam generating, superheating, and resuperheating plant as defined in claim 2 including water injection means connected with said tubular conduit means downstream of said heat exchanger, and means responsive to the temperature of the unexpanded medium downstream of the connection of the outlet of said by-pass conduit with said tubular conduit means and connected with said water injection means for injecting water through the latter into said tubular conduit means when the temperature of the unexpanded medium leaving saidheat exchanger and said by-pass conduit exceeds a predetermined value. v e

a 4. The method of controlling the superheat temperature of relatively high pressure steam and of resuperheating and controlling the resuperheat temperature of relatively low pressure steam comprising heating the relatively low pressure steam by heat transfer from hot combustion gases, subjecting the thus partly superheated relatively low pressure steam to indirect heat exchange with superheated relatively high pressure steam in an indirect heat exchanger, by-passing a relatively great amount of superheated relatively high pressure steam around the heat exchanger for reducing theeffect of the heat exchanger on the relatively high pressure steam, injecting water into the relatively high pressure steam before the relatively high pressure steam enters. the heat exchanger when the temperature of the relatively low pressure stearmafter the relatively low pressure steam has left the heat ex changer, exceeds a predetermined value, and injecting water into the relatively high pressure steam leaving the heat exchanger when the temperature of the reunited relatively high pressure steam by-passing and leaving the heat exchanger exceeds a predetermined value.

5. The method of controlling the superheat temperature of relatively high pressure steam and of resuperheating and controlling the resuperheat temperature of relatively low pressure steam comprising heating the relatively low pressure steam by heat transfer from hot combustion gases, subjecting the thus partly superheated relatively low pressure steam to indirect heat exchange with superheated relatively high pressure steam, injecting water into the relatively high pressure steam before the relatively high pressure steam exchanges heat with the relatively low pressure steam and increasing the amount of the so injected water upon increase of the resuperheat temperature of the relatively low pressure steam above a predermined value and reducing the amount of the so injected water upon decrease of the resuperheat temperature of the relatively low pressure steam below a predetermined value, injecting water into the relatively high pressure steam after the relatively high pressure steam has exchanged heat with the relatively low pressure steam and reducing the amount of the last mentioned injected water upon decrease of the temperature of the relatively high pressure steam below a predetermined value after the relatively high pressure steam has exchanged heat with the relatively low pressure steam and increasing the amount of the last mentioned injected water upon increase of the temperature of the relatively high pressure steam above a predetermined value after the relatively high pressure steam has exchanged heat with the relatively low pressure steam, of reducing the amount of relatively high pressure steam exchanging heat with the relatively low pressure steam when the temperature of the latter is above a desired value before the heat exchange, and of increasing the amount of relatively high pressure steam exchanging heat with the relatively low pressure steam when the temperature of the latter is below a predetermined value.

6. The method of controlling the superheat temperature of relatively high pressure steam and of resuperheating and controlling the resuperheat temperature of relatively low pressure steam comprising heating the relatively low pressure steam by heat transfer from hot combustion gases, subjecting the thus partly superheated relatively low pressure steam to indirect heat exchange with superheated relatively high pressure steam, injecting water into the relatively high pressure steam before the relatively high pressure steam exchanges heat with the relatively low pressure steam and increasing the amount of the so injected water upon increase of the resuperheat temperature of the relatively low pressure steam above a predetermined value and reducing the amount of the so injected water upon decrease of the resuperheat temperature of the relatively low pressure steam below a predetermined value, injecting water into'the relatively high pressure steam after the relativeIy 'high pressure steam has exchanged heat with the relatively low. pressure steam and reducing the amount of the last mentioned :i'nject'ed water upon decrease of the temperature of the relatively high pressure steam below a predetermined value after the relatively high pressure steam has exchanged heat with the relatively low pressure steam and increasing the amount of the last mentioned injectedwater' upon increase of the temperature of the relatively .high pressure steam above a predetermined value after the relatively high pressure steam has exchanged heat with the relatively low pressure steam, and of changing the relative amounts of the heat exchanging relatively high pressure steam and of the relatively low pressure steam according to changes of the relative temperatures of the two steams for supplementing the control of the temperatures of the two steams by the water injection.

ReferencesCited in the file ofthis patent UNITED STATES PATENTS Gilbert -Oet. 15, 1929 Fletcher et al. May 1-, 1951 Kuppenheimer July 8; 1952' Blaskowski Aug. 3, 1954 FOREIGN PATENTS Great Britain July 26, 1 928 .Great Britain June 12, 1930 Great Britain Nov. 17, 1932 Great Britain Apr. 27, 1933 Great Britain Nov. 28, 1951 Germany Apr. 18, 931 

